This invention relates to a boring tool to which a cutting fluid is applied to cool and lubricate cutting tips and guide pad and discharge chips.
In a conventional hollow type boring tool, a compressed cutting fluid is supplied through inside of the boring tool to cool and lubricate cutting tips and the flowing direction of the cutting fluid is changed at the bottom of the bored hole so that chips are discharged to the outside along the outer wall of the boring tool by the streams of the cutting fluid. However, the conventional boring tool has the drawbacks that it is necessary to provide a pump which has a sufficiently high discharge pressure; and the backward flow of the cutting fluid has too weak a force to efficiently draw off chips.
In another known hollow type boring tool, a boring bar has a double tube construction consisting of inner and outer tubes, and the peripheral wall of the outer end of the inner tube is provided with a plurality of holes or slits which are inclined rearward toward the inside of the inner tube. With the latter known boring tool, a cutting fluid is supplied through a space defined between the inner and outer tubes to cool and lubricate cutting tips. This cutting fluid which is now contaminated with chips runs in the opposite direction at the top of the cutter head. Some of the cutting fluid is backward diverted through the holes or slits and runs inside the inner tube toward a proximal end of the boring tool without cooling and lubricating the cutting tips. The afore-mentioned cutting tip-cooling portion of the cutting fluid is drawn out through the inner tube by the absorbing action of the diverted cutting fluid stream. In this case, however, it is necessary to divert about two-thirds of the original amount of a cutting fluid through the holes or slits toward the inside of the inner tube without cooling a cutting tip in order to effectively remove chips entrained with the cutting tip-cooling fluid. In other words, only about one-third of the original amount of the cutting fluid actually contributes to the cooling and lubrication of the cutting tips. Therefore, it is necessary to apply a considerable amount of a cutting fluid and provide a large capacity pump in order to effectively carry out the cooling and lubrication of the cutting tips and also the removal of chips. Sometimes, chips entrained with the circulatively used cutting fluid tend to plug the holes or slits bored in the inner tube. Further, the formation of holes or slits in the inner tube undesirably reduces its mechanical strength. Chips have to be finely broken in order to be easily carried by the cutting fluid. Consequently, the latter type of the known boring tool has its application limited within a relatively narrow range.